I find it logical but at the same time rather fascinating that many zoos in the USA rent koalas for the summer (naturally from San Diego Zoo) and attendance numbers surge as visitors line up to see the sleeping marsupials. On my long road trips through America I almost never see koalas due to their rarity in zoos, but when I went all over Australia in 2007 I became so used to seeing koalas at every single park that I wasn't too concerned about them after a while. The same went for Tasmanian devils, which are surprisingly common at many Aussie zoos.
last year they had just under a hundred (on the census - two were southern, the rest northern), but I imagine it changes all the time if they get in rescue animals.